This invention relates to window shade systems, and more particularly to window shade systems useful for reducing heat transport through windows.
Windows are a conduit through which large amounts of heat are transported into and out of buildings. Buildings gain heat rapidly through windows when the outside air temperature is high, and in winter months when the outside temperature is low, windows constitute one of the largest heat leaks in both residential and commercial structures.
Expensive and complex systems exist to minimize these heat losses and gains. Often, however, such systems are not used because they are expensive, inconvenient to install and operate, and because such systems detract from the aesthetic appearance of the windows in which they are used.
Window shades are among the commonest and least expensive forms of window covering. For these reasons, and because of the ease with which window shades may be installed, they are often replaced to accommodate changing fashions and design modes. An improvement in the insulating quality of window shades can provide a quick and inexpensive reduction of heat flow problems in both residential and commercial buildings.
Conventional window shades permit heat transport through windows by the passage of air between the edges of the shade and window frame. An effective seal between the side edges of the shade and the frame is not provided because the shade must be spaced from the frame to permit upward and downward movement of the shade. Also, just bringing the window shade fully to the bottom of the window opening does not provide an entirely satisfactory insulating seal of the shade against the sill. This is because wooden window frames are often not square or even straight, or because the shade is not hung correctly, so that when the shade contacts the sill in one place, there may still be a gap in other places. Gaps between the shade and sill also result where, as is often the case, the bottom edge contacting surface of the shade has an irregular surface contour which prevents frictional and sealing engagement of the shade against the sill. Such irregularities are commonly caused by warpage of the wooden positioning slat which is affixed to the bottom edge section of the shade.
The prior art has recognized the need for improved energy efficient window shade systems and has provided teachings of systems which reduce the movement of air past the side edges of a shade. In this system, channels are installed along the vertical side walls of the window frame for receiving the side edge sections of the shade. The channels are provided with a generally U-shaped configuration to permit upward and downward movement of the shade, and to provide an insulating seal between the shade and side walls of the frame when the shade is positioned adjacent the sill. A similar channel with its open end facing upward from the window sill could be used for purposes of providing a seal between the sill and bottom longitudinal edge section of the shade. However, provision of a sill channel presents several disadvantages and they have not proved entirely satisfactory. It will be appreciated that such a channel becomes a catcher of dirt and small objects which are difficult to remove. Further, when the wooden positioning slat affixed to the bottom edge of the shade has an irregular curvature, it is difficult to position the bottom edge of the shade within the sill channel. Yet another disadvantage in using the channel at the sill is that the side wall and sill channels must be aligned and installed with precise tolerances in order to provide an insulating seal at the bottom corners of the window frame.